High nitrates with established biopellet reactor

[Djhype97]

First off I just want to say that I'm new to R2R & I'll be starting my thread soon so details on my setup will be included there.

When I upgraded to my 65g 2 years ago I started having nitrate issues. I began vodka dosing, got everything under control and switched to a biopellet reactor. Everything was smooth with keeping NO3 under control until recently. It was time for me to clean the reactor and add more pellets.

Now for the past 2 months NO3 has been steady at 40ppm. I added more pellets when I noticed the NO3 wasn't going down. That was two weeks ago. This past Friday I added 1/4 cup more. I have a total of 2 cups of pellets. As of today my params are:

NO3 40ppm
Po4 .03
ALK 8.8
Cal 460
Mg 1420

My SPS are losing color and not extending polyps. I do not know what move to make now. I've been trying to research and can not find my next move. Please help. Any thoughts, questions or suggestions are appreciated.

 

[mcarroll]

It would be a little surprising if NO3 was causing that. Any chance something else is contributing?

Low PO4, maybe....but you're just borderline, not zero.

Hm

 

[Djhype97]

It would be a little surprising if NO3 was causing that. Any chance something else is contributing?

Low PO4, maybe....but you're just borderline, not zero.

Hm

I tested again just now on the Hanna ULR Phosphorus tester and get .02

 

[mcarroll]

Consider throttling back on your PO4 removal...you might see a decline in your NO3.

I'm guessing, but was your PO4 higher when your carbon dosing seemed to work better?

 

[Salty1962]

Welcome to R2R! How long has your BP reactor been up? It takes a minimum of @ 8 weeks for a BP reactor to become efficient.

 

[Djhype97]

Consider throttling back on your PO4 removal...you might see a decline in your NO3.

I'm guessing, but was your PO4 higher when your carbon dosing seemed to work better?

That's what I thought, so I took GFO offline about 2 weeks ago. Po4 is still low. Should I try to feed more?

Welcome to R2R! How long has your BP reactor been up? It takes a minimum of @ 8 weeks for a BP reactor to become efficient.

The BP reactor has been running for almost a year. It's been almost 2 months since I originally cleaned it out and added more pellets.

 

[Randy Holmes-Farley]

Maybe the nitrate testing is not accurate.

 

[Djhype97]

Maybe the nitrate testing is not accurate.

I've tested at home with 2 different salifert nitrate kits (used a friends kit and my own) an API kit that I have, and took a sample to a Lfs (they tested with API as well) and the salifert is a little difficult to distinguish between the 25 or 50 shade. The API was orange 40ppm.

 

[Djhype97]

I also just found that limewater/kalkwasser can contribute to keeping po4 low? Is this correct?

 

[Randy Holmes-Farley]

I also just found that limewater/kalkwasser can contribute to keeping po4 low? Is this correct?

It might, but I'm not sure it is an especially effective method.

I discuss it here:

What Your Grandmother Never Told You About Lime by Randy Holmes-Farley - Reefkeeping.com
http://reefkeeping.com/issues/2005-01/rhf/index.htm

What Else Does Limewater Do In An Aquarium? Reduce Phosphate

Many reefkeepers accept the concept that adding limewater reduces phosphate levels. This may be true, but the mechanism remains to be demonstrated. Craig Bingman has done a variety of experiments related to this hypothesis, and has published them in the old Aquarium Frontiers. While many aquarists may not care what the mechanism is, knowing it would help to understand the limits of this method, and how it might best be employed.

Habib Sekha (Salifert) has pointed out that limewater additions may lead to substantial precipitation of calcium carbonate in reef aquaria. This idea makes perfect sense. After all, it is certainly not the case that large numbers of reef aquaria will exactly balance calcification needs by replacing all evaporated water with saturated limewater. And yet, many find that calcium and alkalinity levels are stable over long time periods with just that scenario. One way that can be true is if the excess calcium and alkalinity that such additions typically dump into the aquarium are subsequently removed by precipitation of calcium carbonate (such as on heaters, pumps, sand, live rock, etc.).

It is this ongoing precipitation of calcium carbonate, then, that may reduce the phosphate levels: phosphate binds to these growing surfaces, and becomes part of the solid precipitate. The absorption of phosphate from seawater onto aragonite is pH dependent, with the binding maximized at around pH 8.4 and with less binding at lower and higher pH values. If the calcium carbonate crystal is static (not growing), then this process is reversible, and the aragonite can act as a reservoir for phosphate. This reservoir can inhibit the complete removal of excess phosphate from a reef aquarium that has experienced very high phosphate levels, and may permit algae to continue to thrive despite having cut off all external phosphate sources. In such extreme cases, removal of the substrate may even be required.

If the calcium carbonate deposits are growing, then phosphate may get buried in the growing crystal, which can act as a sink for phosphate, at least until that CaCO3 somehow dissolves. Additionally, if these crystals are in the water column (e.g., if they form at the local area where limewater hits the tank water), then they may become coated with organics and be skimmed out of the aquarium.

An alternative mechanism for phosphate reduction via limewater may simply be the precipitation of calcium phosphate, Ca3(PO4)2. The water in many reef aquaria will be supersaturated with this material, as the equilibrium saturation concentration in normal seawater is only 0.002 ppm phosphate. The supersaturation of calcium phosphate will be even higher in the high pH/high calcium fluid present where limewater enters reef aquaria. The locally high pH converts much of the HPO4-- to PO4---, and it is the concentration of PO4--- that ultimately determines supersaturation. That high supersaturation may tip the balance to precipitation of calcium phosphate, just as too much limewater all at once can tip the balance to precipitation of calcium carbonate. As with CaCO3, the precipitation of Ca3(PO4)2 in seawater may be limited more by kinetic factors than by equilibrium factors, so it is impossible to say how much might precipitate under reef tank conditions (without, of course, somehow determining it experimentally).

As with the precipitation of CaCO3 containing some phosphate, if these calcium phosphate crystals are in the water column (e.g., if they form at the local area where limewater hits the tank water), then they may become coated with organics and be skimmed out of the aquarium.